1. Field of the Invention
The present invention relates to a spring-loaded die lifter unit for use in a pressing or punching machine. More particularly, the present invention relates to a spring-loaded die lifter unit floatably provided in the bolster of the machine, wherein the die lifter unit includes a bar-shaped carrier of rollers which carrier is supported by heavy duty springs in grooves extending along the bolster, thereby allowing the die to roll and move smoothly on the rollers.
2. Description of the Prior Art
In a pressing or punching machine for moulding or punching die must be frequently dismounted from the bolster for replacement or repair, but because of its heavy weight it is required to employ a special tool, such as a crane. In order to overcome this difficulty a hydraulic die lifter has been proposed, wherein the die-supporting rollers are hydraulically raised to lift the die above the top surface of the bolster so as to allow the same to smoothly roll thereon.
However, the provision of a hydraulic system in the bolster requires a complicated and troublesome preparatory work, which of course results in an increased production cost. Another disadvantage is that the hydraulic system must be operated each time when the die is mounted or dismounted, which is time- and labor-consuming.
In order to solve such problems of high cost and troublesome operation, a spring-loaded die lifter has been proposed which die lifter includes balls supported on heavy duty springs in their respective holes in the bolster. The balls normally protrude above the top surface of the bolster. When the die is fastened to the bolster by means of hydraulic clamps, the balls are caused to sink below the top surface of the bolster under the oppression by the clamps against the springs.
However, this arrangement requires a lot of boring work which is labor-consuming and costly. In addition, the die is liable to engraved marks caused by the ball surfaces, which tends to bring about undesired play between the die and the bolster. Furthermore, it is disadvantageous in that the balls are likely to drift in their holes, and consequently, it becomes necessary to provide any device so as to hold the balls at rest, which leads to the construction of a complicated and large-sized mechanism. This also increases the production cost.
The present invention is directed toward solving the problems and disadvantages mentioned above, and has for its object to provide an improved die lifter unit operating without the use of any hydraulic power, thereby resulting in a simplified die lifter unit. Another object of the present invention is to provide an improved die lifter without the possibility of damaging the die.
Other objects and advantages of the present invention will become obvious to one skilled in the art from the following description and drawings.